Seam compound update

[Dan McCosh]

I posted a query at the beginning of last summer about using roofing neoprene as a seam compound. I ended up using it for last spring's launch, and after a season it looks awfully good. It seems to bond to the seams better than most of the stuff I'f tried--which most recently has been polysulfide. It sets up and dries quickly, is sandable in a couple of hours vs. days. Seem to have far more elasticity as well. Main drawback so far is it doesn't cut off as cleanly as polysufide when trimming the seams flush--the result of the elasticity. A Fein power scraper is the answer here. Overall, it seems to be a good product. Cost is about one fourth that of polysulfide, which in my case saves about $100 in the spring, which ends up as a bonus. I'm still curious as to whether anyone else has used this stuff. (liquid neoprene roofing caulk)

[Gary E]

Sounds good Dan,

Another use of a product common to every hardware and home store and no "marine" type price tag attached. Did paint stick to it well?

G

[Dan McCosh]

Bottom paint sticks to it just fine. Originally, I bought it to caulk some metal flashing on a bay-window overhang, which also is painted. It does a nice job on roofs as well. Looking up the specs, it also looks good in terms of bonding, elongation, etc.,, although it is supposed to break down in sunlight in 20 years or so. Not sure how much sunlight reflects off the occasional passing carp.

[Wilson Fitt]

I suspect that there is a lot of product development happening in the architectural and construction world that would be useful in boatbuilding.

I used stuff called pitch pan sealant, a two-part, pourable, self levelling commercial roofing product to fill and seal the small space between the side of the keel and the garboards in each frame bay. It is the modern equivelent of hot pitch, has better adhesion and flexibility, is much easier to deal with and more benign from an environmental and health point of view (no carcinegeous fumes or fire risk).

There are high end caulking products that are used to seal aluminium window or curtain wall frames to masonry elements in building exteriors, an area that has large differential expansion rates and is exposed to all types of humidity and temperature extremes. These are not all easy to use or readily available in small quantities, but might bear consideration for a medium or large sized new project.

My point, I guess, is that we should not accept old products and solutions uncritically. They may still be the best, but there are some new things under the sun.

[Dan McCosh]

Actually, virtually all marine sealants, etc., are repackaged from much higher-volume uses such as construction. Sikaflex is huge in construction and automotive adhesives, for example. I tread a little lightly in making substutions, however, on the grounds that some mild reformulation does a lot of good in a special applications such as marine use.

[JormaS]

Sounds very interesting Dan.
Can you give us the name of the product that you used?

[Adam C]

Also Dan,

How does it stick to wood - specifically if you are recaulking old seams with old wood.

[Dan McCosh]

The brand was Dewitts, but others make it as well. It was used on old seams, previously filled mainly with polysulfiede, but with residues of slickseam, and oil-based roofing mastic.

[mariner2k]

Is the "pitch pan sealant" a hot or cold product, and is it removable if needed? Does the roofing neoprene compress with the swelling of the planks. thanks, kevin

[ 01-09-2004, 05:02 PM: Message edited by: mariner2k ]

[Dan McCosh]

The neoprene compresses when the planking swells. It acts pretty much like a piece of medium-soft rubber stuck in the seam. I am trimming off the excess that now stands proud of the seam, after a season in the water.

[ 01-09-2004, 06:08 PM: Message edited by: Dan McCosh ]

[JormaS]

Dan, can you direct us to some web page or other source of more info of Dewitts or equivalent? I tried Google with no success.

[Wilson Fitt]

Pitch pan sealant is a cold product, about the consistency of thick paint before curing and like soft rubber after setting up. Extremely sticky in its liquid form. Not sticky at all when cured but you can easily depress the surface with your finger. It appears to adhere very stongly to almost anything and can only be removed mechanically, ie by cutting or abrasion.

Pitch pans are shallow metal pans without bottoms that are set around penetrations in flat roofs ( vent pipes for instance) and filled up with pitch in the old days to make them waterproof.

[Dan McCosh]

If you look under "neoprene caulk" there are several sources. I can't seem to find what I saw about Dewitt's myself. It is a roofing material, mainly used for metal flashing.

[formerlyknownasprince]

We used a mix of antifouling primer and linseed oil putty in August 2002. We are replacing some of the planks that we repaired with that mix and it has held up brilliantly.

Ian

[Allen Foote]

This is interesting. It's always been hard for me to put any faith in cross-gendered products (building to marine). Tell us in another year how its going. AND is it removable from the seams for plank replacement later? I'm hoping you're not using another 5200 dirivitive.

[formerlyknownasprince]

is it removable

That is exactly what we have just done. Just run the scraper down the remaining plank edge and off it comes.

We used this mix, which Barry (a cabinetmaker by trade, but a boatbuilder by occupation for most of his life) has used for many years to replace Sikaflex that someone else had put in. The Sikaflex had not adhered - which is what you would expect on 65 year old planks.

If I'm not mistaken, the only difference between what we are doing and traditional seam compound is replacing the white lead powder with primer - which helps the paint adhere.

Ian

[Dan McCosh]

Don't know if the question about 5200 was referring to the neoprene or the putty, but the neoprene is not nearly as aggressive an adhesive as 5200. The putty idea is pretty far afield from the neoprene, however. As I noted, one appeal of the neoprene is that it doesn't clog sandpaper when sanding the bottom--one reason why I avoid putty-type seam compounds, as well as asphalt-based compounds. It also works in a power caulking gun, which is important to me in the spring.

[Eddiebou]

I thought about using neopreane to seal up my centerboard trunk a while back. I didn't because I hadn't heard of anyone using it for a purpose like that.
This post was from '04. Any follow-up on it?
I opted for 4200. I didn't want to have to destroy the boat to remove or repair later. Did a little test just for the fun of it:

Oak coated with copper napthanate glued with 5200 showed no problem with setting up or adhesion.

Wh cedar with 4200 just allowed to set, (no clamps) seemed very strong indeed.
Both allowed to cure for a couple of weeks. In both cases, the glued area was only about 3 sq. inches.

Putting 1 of the blocks in a vise, the 4200 gave a respectable fight, but I broke it with hand pressure. It just finally "snapped". The 4200 broke more than the surrounding wood.

The oak blocks were put through the same stress, and did not come apart. I hit it several times with a hammer, and it broke, too.

I was surprised that in both cases, the goo failed before the wood.

[Dan McCosh]

I guess the followup is that I have been using the neoprene for about eight years now and still feel it is the best seam compound I've tried. It goes on easy, can be worked and leveled with a putty knife. It dries quickly, and is easily sanded when dry. It's not supposed to "wet stick", but doesn't seem to be too sensitive to damp wood. Relatively low cost. I have not used it for bedding hardware, but I don't see why it would not work. It is supposed to elongate about 300%, which may be one reason why it seems to stay in the seams fairly well when the hull dries. It also seems to stick to older, oil-based compounds. It is not a glue, as many polyurethanes tend to be. Also, the only color is black.

[mfletch]

I am currently cleaning out the seams of my 26ft carvel planked Buchanen 1950's yacht. I'm very interesting in stopping the seams using your method. The existing seam compound was the usual putty red lead combination.
Do you have any tips on the basic preparation of the seams?
What kind of paint will the neoprene stick best to?
Are you familiar with any common big brand names similar to DeWitts Neo-Seal that may be available in New Zealand? DeWitts don't sell their products down here.
Any general advice will be much appreciated.
Regards,
Mike

[Dan McCosh]

I am currently cleaning out the seams of my 26ft carvel planked Buchanen 1950's yacht. I'm very interesting in stopping the seams using your method. The existing seam compound was the usual putty red lead combination.
Do you have any tips on the basic preparation of the seams?
What kind of paint will the neoprene stick best to?
Are you familiar with any common big brand names similar to DeWitts Neo-Seal that may be available in New Zealand? DeWitts don't sell their products down here.
Any general advice will be much appreciated.
Regards,
Mike

It sticks well to any paint, or dry wood. The stuff is sold as a roof caulking for general use, or for rubber roofs. It is a liquid neoprene rubber compound. It looks like the conventional black tar-based roofing caulk, but is quite different. I would assume it would be made under other brand names, but I don't know what they might be DeWitts is actually a local company, so it is pretty common around here.